Fabrication of One-Dimensionally Oriented Fluorene--Thiophene Copolymer Thin Films and Anisotropic Transistor Characteristics

One-dimensionally oriented poly(9,9-dioctylfluorene- co -bithiophene) (F8T2) thin films with the thickness of approximately 50 nm were deposited by friction-transfer technique. Films were investigated using polarized optical spectroscopy. The dichroic ratio of absorption was estimated to be approximately eight. By means of transmission electron microscope (TEM), we revealed that the main-chains of F8T2 were aligned along the friction direction. Atomic force microscope (AFM) images of as-prepared films showed a roughened surface, whereas the film after subsequent thermal treatment showed remarkably smooth surface. Field-effect transistors utilizing the friction-transferred F8T2 films exhibited a field-effect mobility of $1.88\times 10^{-4}$ cm 2 V -1 s -1 along the friction direction, which is about six times higher than that perpendicular to the friction direction.